双位控制的轮换动作非常频繁,致使系统中的运动部件、如继电器、接触器等触点经常出现火花、容易损坏,而且会影响电机寿命。这样,就很难保证双位式控制系统安全可靠运行。且在生产工艺过程中也并非一定要维持在给定值上,往往只要求液面h保 Double-controlled rotation is very frequent, resulting in the system of moving parts, such as relays, contacts and other contacts often sparks, easily damaged, but also affect the motor life. In this way, it is difficult to ensure safe and reliable operation of two-position control system. And in the production process is not necessarily maintained at a given value, often only require liquid level h Paul